System and method for auto calibration in a power blackout sensing system

Abstract

A calibration amplifier includes: a plurality of transistors and a variable resistor configured to change in response to clock pulses. During a calibration cycle, one of the plurality of transistors switches on in each calibration step based on a plurality of enable signals, and a gain of the calibration amplifier changes until an output voltage of the calibration amplifier exceeds a reference voltage and is set to a calibrated gain. The calibration amplifier outputs the output voltage by amplifying an input voltage using the calibrated gain.

What is claimed is: 
     
       1. A calibration amplifier comprising:
 a plurality of transistors; and 
 a variable resistor configured to change in response to clock pulses, 
 wherein, during a calibration cycle, the plurality of transistors sequentially switch on based on a plurality of enable signals, and a gain of the calibration amplifier changes until an output voltage of the calibration amplifier exceeds a reference voltage and is set to a calibrated gain, and 
 wherein the calibration amplifier outputs the output voltage by amplifying an input voltage using the calibrated gain. 
 
     
     
       2. The calibration amplifier of  claim 1 , wherein the variable resistor comprises a plurality of resistors connected in parallel and to a respective one of the plurality of transistors, and
 wherein each of the plurality of resistors is set to a predetermined resistor value. 
 
     
     
       3. The calibration amplifier of  claim 1 , further comprising a flip-flop counter that generates the plurality of enable signals, and each of the plurality of enable signals corresponds to a respective one of the clock pulses. 
     
     
       4. The calibration amplifier of  claim 1 , wherein the reference voltage is a fixed voltage. 
     
     
       5. The calibration amplifier of  claim 1 , wherein the calibration cycle starts in response to a switch-off signal of a power blackout sensing system. 
     
     
       6. The calibration amplifier of  claim 5 , wherein the power blackout sensing system comprises a voltage comparator that outputs a sensor voltage signal based on a comparison between the output voltage of the calibration amplifier and a voltage of a neutral wire, and
 wherein the sensor voltage signal is a voltage of a secondary power source during a switch-on period and a switch-off period. 
 
     
     
       7. The calibration amplifier of  claim 6 , wherein the reference voltage is determined based on a voltage of the secondary power source. 
     
     
       8. The calibration amplifier of  claim 6 , wherein the sensor voltage signal remains low after the output voltage of the calibration amplifier exceeds the reference voltage. 
     
     
       9. The calibration amplifier of  claim 8 , wherein the sensor voltage signal is high during a blackout period regardless of the switch-on period or the switch-off period indicating a power outage condition. 
     
     
       10. The calibration amplifier of  claim 6 , wherein the power blackout sensing system further comprises an AC-to-DC (ADC) converter, and the input voltage of the calibration amplifier is an output voltage of the ADC converter. 
     
     
       11. A power blackout sensing system comprising:
 a voltage regulator configured to receive one of three phase wires and a neutral wire of a primary power source that provides an alternating current (AC) power; 
 a calibration amplifier comprising a plurality of transistors and a variable resistor that is configured to change in response to clock pulses; 
 a voltage sense amplifier; 
 a sensing block configured to receive the neutral wire of the primary power source and comprising a coupled inductor device and the voltage sense amplifier; and 
 a secondary power source, 
 wherein the voltage regulator is coupled to a switch and generates a direct current (DC) voltage signal, and 
 wherein the coupled inductor device of the sensing block comprises a pull-down resistor, wherein the coupled inductor device is configured to convert a voltage signal of the neutral wire to a 180-degree phase-shifted voltage signal of the neutral wire and generate a reference voltage signal using the pull-down resistor, 
 wherein the voltage sense amplifier is configured to amplify a voltage gap between the 180-degree phase-shifted voltage signal of the neutral wire and the reference voltage signal, 
 wherein, during a calibration cycle, the plurality of transistors of the calibration amplifier sequentially switch on based on a plurality of enable signals, and a gain of the calibration amplifier changes until an output voltage of the calibration amplifier exceeds the reference voltage and is set to a calibrated gain, 
 wherein the calibration amplifier outputs the output voltage by amplifying an input voltage using the calibrated gain, and 
 wherein the sensing block detects a phantom voltage on the one of three phase wires and provides an output signal corresponding the secondary power source during a blackout period. 
 
     
     
       12. The power blackout sensing system of  claim 11 , further comprises a voltage comparator that is configured to output a sensor voltage signal, wherein the sensor voltage signal is a voltage of the secondary power source during a switch-on period and a switch-off period, and the sensor voltage signal is zero during the blackout period. 
     
     
       13. The power blackout sensing system of  claim 12 , wherein the sensor voltage signal remains low after the output voltage of the calibration amplifier exceeds the reference voltage. 
     
     
       14. The power blackout sensing system of  claim 13 , wherein the sensor voltage signal is high during a blackout period regardless of the switch-on period or the switch-off period indicating a power outage condition. 
     
     
       15. The power blackout sensing system of  claim 11 , wherein the variable resistor of the calibration amplifier comprises a plurality of resistors connected in parallel and to a respective one of the plurality of transistors, and wherein each of the plurality of resistors is set to a predetermined resistor value. 
     
     
       16. The power blackout sensing system of  claim 11 , wherein the calibration amplifier further comprises a flip-flop counter that generates the plurality of enable signals, and each of the plurality of enable signals corresponds to a respective one of the clock pulses. 
     
     
       17. The power blackout sensing system of  claim 11 , wherein the reference voltage is a fixed voltage. 
     
     
       18. The power blackout sensing system of  claim 11 , wherein the calibration cycle starts in response to a switch-off signal. 
     
     
       19. The power blackout sensing system of  claim 11 , wherein the reference voltage is determined based on a voltage of the secondary power source. 
     
     
       20. The power blackout sensing system of  claim 11 , wherein the power blackout sensing system further comprises an AC-to-DC (ADC) converter, wherein the ADC converter receives an AC voltage from the voltage sense amplifier and provides a DC voltage to the calibration amplifier as the input voltage of the calibration amplifier.